Python is …

How to learn Programming?

Three inconvenient truths 😰

• programming cannot be learnt in a course alone
  • I try to make the start as easy as possible!
• frustration is part of learning
  • fight your way!
• the Python ecosystem is huge
  • grow skills by step-by-step

. . .

Programming can be absolutely captivating! ✌️

Variables

Variables are kind of storage boxes 🎁

# define variables
x = "at your service"
y = 2
z = ", most of the time."

# combine variables
int_combo = y * y       # for numbers any mathematical operation
str_combo = x + z       # for text only concatenation with +

# show content of variable
print(str_combo)

Data Types

The type defines the object’s properties

Data Type Conversion

Combine variables of the same type only

# check the type
type(YOUR_VARIABLE)

# convert types (similar for other types)
int('100')  # convert to integer
str(100)    # convert to string

# easiest way to use a number in a text
x = 3
mixed = f"x has the value: {x}"
print(mixed)

Confusing Equal-Sign

= vs. == contradicts the intuition

# assign a value to a variable
x = 1
word = "Test"

# compare two values if they are identical
1 == 2              # False
word == "Test"      # True

Comments

• lines ignored by Python
• write comments, it helps you… 📝
  • to learn initially
  • to understand later

# single line comment

"""
comment across 
multiple 
lines
"""

Visual Studio Code

The (best) editor to program in Python

TODO: better Intro in editor

In-class: Get started for Python

1. Make sure that your local copy of the Github repository KED2024 is up-to-date with git pull in your command-line.
   
2. Open the Visual Studio Editor.
3. Windows User only: Make sure that you are connected to WSL: Ubuntu (green badge lower-left corner, see image on the slide after the next). If not, click on the badge and select New WSL Window.

In-class: Run your first Python Program

1. Create a new file with the following content, save it as hello_world.py in the KED2024 folder. Then, execute it by a right click on the code and select Run current file in interactive window.

   # print out a message
   msg = "Hello World!"
   print(msg)

2. Does the output looks like the screenshot on the next slide? If the execution doesn’t work as expected, ask me or your neighbour. There might be a technical issue.

In-class: Expected Output

The Output “Hello World!” on the right side should look like in the screenshot

Iterations

for-loop

do something with each element of a collection

sentence = ['This', 'is', 'a', 'sentence']

# iterate over each element
for token in sentence:
    
    # do something with the element
    print(token)    

Conditionals

if-else statement

condition action on variable content

sentence = ['This', 'is', 'a', 'sentence']

if len(sentence) < 3:
    print('This sentence is shorter than 3 tokens')
    
elif len(sentence) == 3:
    print('This sentence has exactly 3 tokens')
    
else:
    print('This sentence is longer than 3 tokens')

Indentation matters!

if 5 > 2:
    print('5 is greater than 2')

if 5 > 2:
print('5 is greater than 2')

Methods: Create new Objects

Build your world! 🌍

sentence = 'This is a sentence'

# split at whitespace and save result in new variable
tokens = sentence.split(' ')    

# check the content and type variables
print(sentence, type(sentence), tokens, type(tokens))           

Methods: Change Objects

Depending on the object, you can do different things 🛠️

# add something to a list
tokens.append('.')

# concatenate elements to string
tokens = ' '.join(tokens)
print(tokens, type(tokens))

Functions and Arguments

DRY: Don’t Repeat Yourself

• functions have a name and optional arguments
  • function_name(arg1, ..., argn)
• some functions are predefined
  • print(), len() and sorted()

def get_word_properties(word): # define function
    """
    Print properties for a word given as an argument.
    """
    length = len(word)
    sorted_letters = sorted(word, reverse=True)
    print(f"{word} has {length} letters ({sorted_letters})".)

get_word_properties('computer') # call function with any word

Indexing

Computers start counting from zero! 😵

sentence = ['This', 'is', 'a', 'sentence']

# element at position X
first_tok = sentence[0]     # 'This'

# elements of subsequence [start:end]
sub_seq = sentence[0:3]     # ['This', 'is', 'a']

# elements of subsequence backwards
sub_seq_back = sentence[-2:]        # ['a', 'sentence']

Errors

A myriad of things can go wrong 🤦

Modules/Packages

No programming from scratch 🎉

• packages provide more objects and functions
• packages need to be installed additionally

# import third-party package
import pandas
import spacy
import plotnine

Jupyter Notebooks

• combine text and code in a single document
  • similar to R Markdown
• open in VS Code
• run code with the play button left to the cell or with CTRL+Enter

In-class: Exercises I

1. Open the script with the basics of Python in your Visual Studio Editor:
   KED2024/materials/code/python_basics.ipynb
2. Try to understand the code in each cell and run them by clicking the play symbol left to them. Check the output. Modify some code as well as data and see how the output changes. Initially, this try-and-error is good strategy to learn. Some ideas:
   • Combine a string and an integer variable without converting it. What error do you get? How can you avoid it?
   • Select is a from the variable sentence using the right index.

In-class: Exercises II

1. Write a Python script that

   • takes text (a string)
   • splits it into words (a list)
   • iterates over all the tokens and print all tokens that are longer than 5 characters
   • Bonus: wrap your code in a function.

2. Go to the next slide. Start with some of the great interactive exercises out there in the web.

Resources